Preheat the oven to 350 degrees Fahrenheit. Line a cupcake/muffin pan with cupcake liners. Set aside.

Melt the butter and chocolate together in the microwave. Microwave in 30 second increments, stirring between each time. You may also melt the butter and chocolate over low heat on the stovetop. Stir until smooth and set aside to slightly cool.

In a medium sized bowl, toss the cocoa powder, flour, baking soda, baking powder, and salt together until thoroughly combined. Set aside. In a large bowl, whisk the eggs, sugar, brown sugar, and vanilla together until smooth. Add the cooled butter/chocolate and whisk until smooth. Add half of the flour mixture, then half of the buttermilk. Repeat until everything is added. Stir until *just* combined; do not overmix. The batter will be very thick like pudding.

Fill cupcake liners 1/2 full. Bake for 18 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before frosting.

For the vanilla frosting

Cream softened butter on medium speed for about 3 minutes. Slowly add powdered sugar and beat with mixer until combined.